Flow through a Collapsible Tube: Experimental Analysis and Mathematical Model

Flow through thin-wall axisymmetric tubes has long been of interest to physiologists. Analysis is complicated by the fact that such tubes will collapse when the transmural pressure (internal minus external pressure) is near zero. Because of the absence of any body of related knowledge in other sciences or engineering, previous workers have directed their efforts towards experimental studies of flow in collapsible tubes. More recently, some attention has been given towards analytical studies. Results of an extensive series of experiments show that the significant system parameter is transmural pressure. The cross-sectional area of the tube depends upon the transmural pressure, and changes in cross-section in turn affect the flow geometry. Based on experimental studies, a lumped parameter system model is proposed for the collapsible tube. The mathematical model is simulated on a hybrid computer. Experimental data were used to define the functional relationship between cross-sectional area and transmural pressure as well as the relation between the energy loss coefficient and cross-sectional area. Computer results confirm the validity of the model for both steady and transient flow conditions.     

Potentials of spinal motoneurons in cats with experimental tetanus

Potentials of motoneurons of the lower segments of the spinal cord were recorded with the aid of intracellular microelectrodes in experiments on cats with induced tetanus produced by injection of tetanus toxin (1500–2000 mouse LD₅₀) into the extensor muscles of the left shin. Neither afferent volleys of impulses in cutaneous and muscle nerves, nor antidromic volleys in the corresponding ventral roots, produced IPSPs in motoneurons of the extremity into which toxin was injected. The form both of antidromic peak potentials and of monosynaptic EPSPs in motoneurons in which IPSPs were blocked by tetanus toxin did not differ from the form of corresponding potentials of motoneurons in normal cats. The values of threshold depolarization for peak discharges during synaptic and direct stimulation were equal in tetanus and control motoneurons. Resistance and time constant values of the membrane in "tetanus" motoneurons did not differ from the corresponding values for "control" motoneurons.N. I. Pirogov Second Medical Institute, Moscow. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 25–34, July–August, 1969.     

Corticofugal influences on neurons of the main trigeminal sensory nucleus

The effects of stimulation of the ipsilateral sensomotor cortex were studied on 88 neurons in the region of the main trigeminal sensory nucleus of a cat. The cortex was stimulated via a coaxial electrode by single impulses. Stimulation of the cortex caused the appearance of EPSPs and action potentials in these neurons; a small number of these responses were monosynaptic. The polarity of the impulse applied to the cortex had a significant effect on the magnitude of the latent period of the response and the postsynaptic reaction, which is apparently caused by the stimulation of different types of cortex neurons. Apparently, corticofugal pulsation regulates the level of sensitivity of the trigeminal sensory neurons.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 47–53, July–August, 1969.     

Vasoactive properties of dihomo-gamma-linolenic acid and series one prostaglandins in a freshwater teleost, Channa maculata

1. Prostaglandins A1, B1, E1 and F1 alpha (2-120 micrograms/kg), arachidonic acid and dihomo-gamma-linolenic acid (0.1-2 mg/kg) were injected intravenously into Channa maculata and changes in arterial blood pressure were recorded. 2. Injection of PGF1 alpha had no significant effect on arterial blood pressure. Injection of PGA1 and PGE1 was followed by dose-dependent hypotension whereas injection of PGB1 elicited significant dose-dependent increase in arterial blood pressure. 3. Both dihomo-gamma-linolenic acid and arachidonic acid were also depressor agents but dihomo-gamma-linolenic acid was more potent. 4. A single bolus intravenous injection of indomethacin (5 mg/kg) or 4 daily intraperitoneal injections (4 x 10 mg/kg) significantly lowered arterial blood pressure. One hour after pre-treatment of indomethacin, the vascular effects of both prostaglandin precursors were abolished. 5. It appears that the vascular effects of prostaglandins in Channa maculata are qualitatively different from those reported for mammals.     

Functional vasoactive intestinal polypeptide (VIP) receptors in human neuroblastoma subclones that contain VIP precursor mRNA and release VIP-like substances

Three phenotypically distinct subclones (SH-SY-5Y, SH-EP, SH-IN) of the human neuroblastoma cell line SK-N-SH were found to possess vasoactive intestinal polypeptide (VIP) precursor mRNA, release immunoreactive VIP, and express high-affinity VIP receptors coupled to adenylate cyclase. The apparent molecular mass for the receptor polypeptide, as determined by covalent cross-linking of 125I-VIP, was 49 kDa. After 2 days in culture, a concentration of immunoreactive VIP equivalent to the binding affinity of VIP to its receptor was found in the medium in two of these clones (SH-IN and SH-EP). Conditioned medium from SH-IN cells competitively displaced 125I-VIP binding and increased cAMP levels in SH-EP cells, indicating that all of the necessary components for a potential autocrine action of VIP exist in SK-N-SH cells. After numerous cell passages, the SH-EP subclone converted to a distinct phenotype in which VIP precursor mRNA and VIP immunoreactivity in the cell and medium were no longer detectable. In correlation, the VIP receptor number increased, and the EC50 for VIP stimulation of cAMP production shifted to a lower concentration. This points to the possibility that the continuous presence of endogenous VIP in earlier passage SH-EP cells causes a modification in VIP receptor number and cell responsiveness to VIP.